Abstract:

Alpine plants show unique functional plasticity in the process of adapting to environmental constraints such as high altitude， low atmospheric pressure and a short growing season. This research explored the morphological variation in twigs and leaves of Rhododendron capitatum along an altitude gradient to evaluate the functional significance of this variation for resource acquisition， survival and reproduction. In August 2019， various leaf and twig traits of 23 groups of R.capitatum were measured at altitudes from 3400-3700 m. It was found that with increase in altitude， the leaf dry matter content （LDMC）， density （LDE）， thickness （LT） and total leaf dry matter content （TLDMC） were increased. Leaf length （LL）， width （LW）， area （LA）， volume （LV）， dry weight （LDW）， stem length （SL）， stem dry weight （SDW）， total leaf dry weight （TLDW）， total leaf area （TLA）， stem slender ratio （SSR） and stem volume （SV） showed a “V” shaped altitudinal trend with the lowest values at around 3600 m altitude. Higher altitude significantly increased thickness （LT）， dry matter content （LDMC）， density （LDE）， but significantly decreased specific leaf area （SLA）， total leaf area （TLA） and total specific leaf area （TSLA）， respectively. There were significant correlations between most measured traits. The variance components of leaf traits between R. capitatum plants growing at the same altitude were significantly higher than those between plants at different altitudes. The smallest coefficient of phenotypic differentiation of twigs and leaves was 3.19% for stem dry matter content （SDMC）， the largest was 57.73% for leaf density （LDE）， and the average across traits was 20.65%. The results show that some traits of R. capitatum are not sensitive to elevation changes， and that a few key traits like leaf area （LA）， specific leaf area （SLA）， leaf dry matter content （LDMC） and leaf density （LDE） act as functional traits to adapt to alpine habitats. R. capitatum showed lower phenotypic variation among plants along elevation gradients than among plants at the same altitude.

Key words: alpine, functional traits, altitude, phenotype differentiation, Rhododendron capitatum